1. Field of the Invention
The present invention relates to an antireflective film used for exposure of a resist layer in a process for manufacturing a semiconductor device, and an exposure method using the antireflective film.
2. Description of the Related Art
In the field of semiconductor devices, it has been urgent to establish a new process technique permitting processing of submicron patterns of, for example, 65 nm or less. A so-called photolithographic technique may be required for processing submicron patterns, and an argon-fluoride (ArF) excimer laser at a wavelength of 193 nm is currently used as an exposure light source in order to improve optical resolution and comply with submicron processing by shortening the wavelength of exposure light (illuminating light).
A silicon semiconductor substrate is patterned using a photosensitive resist layer which is formed by applying on a surface of the silicon semiconductor substrate coated with an oxide film. However, when exposure light (illuminating light) has high reflectance at an interface between the resist layer and the silicon oxide film used as an underlying layer, a stationary wave is significantly induced in the resist layer. As a result, the sides of the resist layer patterned by development have irregularity according to the shape of the stationary wave, thereby causing the problem of failing to form a satisfactory rectangular pattern in the resist layer. The pattern formed in the resist layer may be referred to as a “resist pattern”. For example, when a resist layer having a refractive index of 1.70 is provided on a silicon oxide film of 100 nm in thickness formed on a surface of a silicon semiconductor substrate, the reflectance of exposure light at a wavelength of 193 nm is as high as about 70% in vertical incidence of the exposure light.
In order to resolve the above-mentioned problem, in a photolithographic technique using usual exposure light at a wavelength of 193 nm, a single-layer antireflective film is formed between a silicon semiconductor substrate and a resist layer. For example, when a resist layer having a refractive index of 1.70 is formed on an antireflective film having a thickness of 100 nm and a complex refractive index N0 (=no−k0i wherein no=1.75 and k0=0.30), which is formed on a silicon oxide film of 100 nm in thickness formed on a surface of a silicon semiconductor substrate, the reflectance at the interface between the resist layer and the antireflective film is greatly decreased to about 1% in vertical incidence of exposure light.